1Gas and Dust in Gas and Dust in interstellar spaceinterstellar spacePSC 203PSC 203OverviewOverviewWhat is interstellar space?What is interstellar space?What is out there?What is out there?What do those things look like?What do those things look like?Interstellar spacewhat do you think this term means?what do you think this term means?““the region between the starsthe region between the stars””Distances between stars are largeDistances between stars are largeThatThat’’s a lot of space !s a lot of space !Interstellar space““the region between the starsthe region between the stars””is it empty?is it empty?almost but not completelyalmost but not completelyso what is out there? so what is out there? gasgasdustdustAlmost empty?empty is really a description of densityempty is really a description of densityempty would be: density = 0 empty would be: density = 0 Typical Densitieswater = water = 1 g/cm1 g/cm33air = air = 0.00125 g/cm0.00125 g/cm33in 1 g of water or air there are a lot of in 1 g of water or air there are a lot of moleculesmoleculeswater = 3.3 x 10water = 3.3 x 102222molecules/cmmolecules/cm33air = 2.6 x 10air = 2.6 x 1019 19 molecules/cmmolecules/cm332DensitiesInterstellar gasInterstellar gasHydrogen = 0.01 atoms/cmHydrogen = 0.01 atoms/cm331 Hydrogen atom in 100 cm1 Hydrogen atom in 100 cm33Interstellar dustInterstellar dustdust = 1 x 10dust = 1 x 10--12 12 particles/cmparticles/cm331 dust particle in 1,000,000 m1 dust particle in 1,000,000 m33Densitiesspace is not empty, just a very low space is not empty, just a very low densitydensitycompared to air, compared to air, space is almost emptyspace is almost emptyHigher density regionsHigher density regionsair can have clouds of higher densityair can have clouds of higher densityinterstellar space also has cloudsinterstellar space also has cloudsNebulae““clouds of dust and gas in spaceclouds of dust and gas in space””one is called one is called ““nebulanebula””more than one is called more than one is called ““nebulaenebulae””CompositionCompositionWhat are the clouds made of?What are the clouds made of?Mostly hydrogenMostly hydrogenTrace amounts of other gasesTrace amounts of other gasesDust is mainly carbonDust is mainly carbonNebula SizesNebula Sizessmaller smaller ––10 light years across10 light years acrosslarger larger ––200 light years across200 light years across3LocationsLocationsSome nebula are associated with starsSome nebula are associated with starsWe have already talked about 3We have already talked about 3Star formation regionsStar formation regionsPlanetary nebulaPlanetary nebulaSupernova remnantsSupernova remnantsStar formationStar formationPlanetary NebulaPlanetary NebulaSupernova remnantSupernova remnantAppearance typesAppearance typesNebulae are also categorized based on Nebulae are also categorized based on appearanceappearanceThree main typesThree main typesDarkDarkReflectionReflectionEmissionEmissionDark nebulaedense cloud of dust and gas blocks out dense cloud of dust and gas blocks out light coming from behind the cloudlight coming from behind the cloudcan block out stars or another nebulacan block out stars or another nebula4Dark nebulaeDark nebulaeVisible Visible vsvsIRIRInfraInfra--red light can pass through the dustred light can pass through the dustReflectionReflectionlight from a nearby star reflects off light from a nearby star reflects off nebula toward usnebula toward usreflection is diffuse or reflection is diffuse or ““scatteringscattering””blue light scatters bestblue light scatters bestReflectionReflectionEmissionEmissionlight from a nearby star causes nebula to light from a nearby star causes nebula to emit lightemit lightemission can be many emission can be many colorscolorsHydrogen emits in reddish purple lightHydrogen emits in reddish purple lightbut blue is scattered, so mostly red is leftbut blue is scattered, so mostly red is leftEmissionEmission5EmissionEmissionCombinationCombinationquite often you can see more than one quite often you can see more than one type of nebula in the same regiontype of nebula in the same regionreflection nebula from gas behind starreflection nebula from gas behind staremission nebula from gas in front of staremission nebula from gas in front of stardark clouds higher density regions in dark clouds higher density regions in frontfrontCombinationCombinationIn-Class Activity:●In small groups, discuss●For each of the following images, does it show–dark nebula–emission nebula–reflection nebula–Combination (identify which types)●Then we will discuss as a